Generally, the motor-driven foldable type door mirror comprises a mirror base fixed to the door of a car, a shaft integrally formed on and extending from the mirror base, a mirror assembly pivotably supported on the shaft, a motor installed in the mirror assembly, and a reduction gear mechanism and clutch mechanism disposed between the motor and shaft. When the motor is put into operation, the mirror assembly is pivoted in relation to the mirror base from the normal to folded position or vice versa.
In such motor-driven foldable type door mirror, it is important to set an appropriate value of the output torque, namely, the reduction ratio of the reduction gear mechanism, for a smooth pivoting of the mirror assembly between the normal and folded positions. Also it is essential to design a compact drive and speed reduction mechanisms in the mirror assembly.
One of the motor-driven foldable type door mirrors having a compact structure and a large reduction ratio is known from the Japanese Unexamined Patent Publication No. Sho 62-50249 (laid open on Mar. 4, 1987).
This motor-driven foldable type door mirror comprises a reduction gear mechanism having two sets of a worm and worm wheel, which provides for a compact design and a large reduction ratio.
The present invention has an object to provide a motor-driven foldable type door mirror with no mutual interference between the reduction gear mechanism and clutch mechanism and having a larger reduction ratio.
The present invention has another object to provide a motor-driven foldable type door mirror in which it is possible to minimize the abrasion of both ends of the rotating shaft of the second-stage worm as well as the abrasion of the thrust bearing bearing the shaft ends.
The present invention has a still another object to provide a motor-driven foldable type door mirror in which the first-stage worm wheel or second-stage worm is not influenced by the thrust load developed at the counterpart, namely, the second-stage worm or first-stage worm wheel, while it is possible to prevent the speed-reduction efficiency of the reduction gear mechanism from being lowered due to the thrust load.
The present invention has a further object to provide a motor-driven foldable type door mirror which can be manufactured with a reduced quantity of necessary component parts and a reduced number of assembling processes.